Regulated power supplies, including switched mode power supplies (SMPSs) are found in numerous electronic systems and devices. Despite the efficiency advantages of SMPSs over, for example, linear power supplies, they are known to introduce significant radiated losses during switching operations. In particular, SMPSs are limited in efficiency by “hard switching” (i.e. switching at non-zero volts) topologies and parasitic power dissipation in their associated magnetic components. In these topologies, switching causes a rapid transition in the current through the switch, such as a transistor, resulting in losses in the form of signal emissions. Moreover, these switching transients may include a spectrum containing high frequency components, which can introduce noise into the system in addition to the power losses.
In order to reduce these losses, “soft switching” topologies exist which utilize either resonant edge or half sinusoid waveforms to operate the switches in a zero voltage switching (ZVS) mode (i.e. zero volts at the time of switching). For example, a resonator may be used to force the current in the transistor to zero during the switching period. This reduces or eliminates switching transients and the radiated emissions caused by rapid transitions in the current. However, these methods incorporate time-consuming waveform changes within a switching period that may limit applications to lower switching frequencies (e.g. 50-200 kHz). These lowered switching frequencies prevent size and weight reductions of the magnetic components, both of which may decrease as the operating frequency rises.
Further, the use of half sinusoid resonant pulses (or a section thereof) as a fixed-area pulse requires the supply to utilize pulse frequency modulation (PFM) at a fixed duty cycle in order to control its average output. However, varying the operating frequency of the PWM controller is undesirable in many applications, such as RADAR systems and other military power supplies.
Alternative pulse width modulated SMPSs and control methods are desired.